1. Field of Invention
The invention relates to an interface unit, and more particularly to an interface unit connectible to a parallel interface of data communication equipment or to a parallel interface of data terminal equipment.
2. Discussion of Related Art
A data communication system comprises a data communication equipment (DCE) and a data termination equipment (DTE), as shown in FIG. 1. Various data interfaces have been developed for different applications of the DCE. Most of these interfaces are internationally standardized. Such electrical and functional interfaces include the standards V.28, V.11, V.35, X.21 or G.703 of CCITT. These standard interfaces differ from each other with respect to their use, because various speed requirements have produced a great variety of electrical realizations requiring varying numbers of parallel connection signals and mechanical terminals of different kinds.
A frequent problem with data communication systems comprising several different interfaces is the small maximum range of transmission (e.g. 10 m), as a result of which the data terminal equipment has to be disposed close to the data communication device even though a considerably greater range of transmission would often be required.
Moreover, all signals in a typical standard interface are in parallel form, and, at worst, a connection cable, such as the connection cable 21 in FIG. 2, may comprise tens of parallel conductors. A cable of this kind is expensive and difficult to install.
In an attempt to solve these problems, U.S. Pat. No. 4,734,696 suggests that instead of being transmitted in parallel form, as usual, connection signals should be converted into series form outside the device through time-division multiplexing with a separate unit, and transmitted in serial form from the data communication equipment through a connection cable into an interface unit disposed in the immediate vicinity of another device to the attached to it. In the interface unit, the serial signal is again converted into a parallel connection signal which is applied to the other device.
However, there remains the problem that either a data terminal equipment DTE directly or another data communication equipment DCE, such as a modem, can be connected to the data communication equipment DCE. In FIG. 1, for example, a terminal equipment 5 and a modem 6 are connected directly to a data communication equipment 4. This causes problems in the matching of the interface with the equipments, as the connection of the connection signals is different in both cases. This requires several different interface units or modifications to be carried out at the installation step.